One thing I think Doomsday needs is the ability to drop items like Ammo and Weapons in CO-OP games to share with other players. As far as I can see there is no way to do that. Also related to that, perhaps a way to give health to other players would be nice.

In my opinion this is something I would expect to see in a mod rather than an explicit feature. Once Doomsday Script has the requisite bindings I can think of no reason for this to be implemented internally.